1. Field of the Invention
The present invention generally relates to a brake assembly and to a method for braking a vehicle or another selectively movable assembly and more particularly, to a brake assembly which provides a controllably varying amount of self-energization.
2. Background of the Invention
A self-energizing braking system, such as and without limitation that which is shown and described in European Patent Number EP 0953785A3 which is fully and completely incorporated herein by reference, word for word and paragraph for paragraph, generally includes an actuator (e.g., a motor) which selectively provides an actuation force in response to a sensed movement or depression of a braking member, and a self-energization member having at least one wedge portion having a certain fixed angle of inclination which assists in the braking of the selectively movable assembly (e.g., a vehicle) within which the braking system is operatively deployed. It should be realized, at the outset, that while the terms vehicle and selectively movable assembly may be interchangeably used throughout this description, nothing in this description is meant to limit the present invention to a particular type of selectively movable assembly, such as a vehicle. In fact, the present invention may be selectively used in a wide variety of selectively movable assemblies, including but not limited to vehicles.
Particularly, the actuation force is typically applied to a pad member and causes the pad member to then engage a portion of the self-energizing braking system (e.g., a rotor) which is attached to a moving wheel, thereby frictionally braking the selectively movable assembly. Particularly, the at least one wedge portion of the self-energization member assists in braking the vehicle (or other selectively movable assembly) by transferring the frictional force (created by the engagement of the pad to the rotor) from a force parallel to the rotor face into a force perpendicular to the rotor face, effectively magnifying the frictional force, thereby desirably reducing the overall actuation force needed to brake the selectively movable assembly in a desired manner. Importantly, the geometric or physical characteristics (e.g., the angle of inclination) of the at least one wedge portion of the self-energization member allows this increase in frictional force to occur without the use of additional actuation energy, thereby conserving energy by actually reducing the overall amount of actuation energy required from the motor and/or from the operator of the vehicle or the selectively movable assembly in order to brake the selectively movable assembly.
The self-energizing braking system can be designed to operate in two different modes. In one, the “compression” mode, the force generated by the motor and/or operator acts on the pad in the same direction as the frictional force. The frictional force pushes the pad into the wedge, increasing the normal force between the pad and the rotor and therefore increasing the friction. In the second, the “tension” mode, the frictional force alone is great enough to engage the brake fully (creating theoretically infinite braking force), and the motor and/or operator pushes in the opposite direction as the friction in an effort to reduce the wedging action and therefore reduce the amount of friction created.
While the foregoing conventional self-energizing braking system does desirably reduce the amount of actuating force needed to brake a selectively movable assembly, it has some drawbacks.
For example and without limitation, this approach does not allow for the use of a relatively low powered motor since the motor must be capable of operating under conditions in which the amount of friction between the rotor and the pad is relatively high and when the amount of friction between the rotor and the pad is relatively low.
For example, in a compression mode of operation, (i.e., in an operational mode in which the direction of rotor travel and the input force to the pad are in the same direction), should the friction be relatively low, the gain obtained from the self-energization is typically undesirably low and the motor must work relatively hard to achieve the desired braking of the vehicle. An undersized motor (e.g., a motor which does not provide enough actuation force to ensure desired operation in high and low friction conditions) may not generate the amount of deceleration required by the operator.
Moreover, should the friction be relatively high while the braking assembly is in a compression mode of operation, the electromechanical braking system may undesirably enter into a tension mode of operation (i.e., a mode in which the direction of rotor travel and the input force to the pad are in opposite directions) which may cause an inconsistent braking feel or may even cause an undesirably high amount of braking force to be generated.
During a tension mode of operation, which occurs when the frictional force is relatively high, an undersized motor may not be able to pull the pad with enough force to prevent it from being frictionally locked onto the rotor. Also, if the friction is too low, while the braking assembly is in a tension mode of operation, the electromechanical braking system may undesirably enter a compression mode of operation.
Hence, a current or conventional self-energization braking configuration provides the desired self-energization by the use of at least one wedge portion having a fixed angle of inclination and being mounted to the pad. As earlier delineated, the fixed inclination angle of the wedge allows the wedge to force the pad against the rotor in order to assist the motor in braking the moving assembly. In the current or conventional self-energization braking configuration, the angle of inclination of the wedge may not be too low since, if it were, a high level of friction could cause the electromechanical braking system to go from a compression mode of operation to a tension mode of operation. This transition from one mode of operation to another can create problems for the controller of the system and may be undesirable. If the wedge angle were too high, the effects of self-energization would be too small, leading to more inefficient use of the motor.
Moreover, as the pad wears during continued operation of the selectively movable assembly, the position of the wedge changes, thereby causing the amount of provided self-energization or “self-energization gain” to uncontrollably vary, causing the system to deviate from the optimum operating levels for energy efficiency.
The present invention addresses these and other drawbacks in a new and novel fashion and represents a braking assembly having a controllably varying amount of self-energization.